1. Field of the Invention
The present general inventive concept relates to an image forming apparatus, and more particularly, to an image forming apparatus in which a paper loading tray has an improved lifting and/or lowering structure to load one or more sheets of paper as a printing medium.
2. Description of the Related Art
An image forming apparatus is configured to print an image on a sheet of paper as a printing medium on the basis of an image signal inputted into the image forming apparatus. The image forming apparatus generally includes a body defining the outer appearance of the image forming apparatus, a paper feeding unit to automatically feed sheets of paper, a printing unit to apply toner or ink, selected depending on a printing manner, onto each fed sheet of paper and form an image on the fed sheet of paper, and a paper discharge unit to discharge the printed sheet of paper out of the body.
The paper feeding unit includes a paper loading tray to load, therein, the sheets of paper to be fed and a lifting device to lift the paper loading tray toward a pickup roller upon receiving power from a motor. The sheets of paper loaded in the paper loading tray are picked up one by one by the pickup roller and transported to the printing unit.
An example of the image forming apparatus having the above described paper feeding unit is disclosed in Korean Patent Laid-open Publication No. 2005-0019416. The disclosed image forming apparatus includes a motor as a drive source, a cam installed below a paper loading tray to lift or lower the paper loading tray upon receiving power from the motor, and a power transmission mechanism (for example, a series of reduction gears) to reduce the power from the motor and transmit the reduced power to the cam. If the motor rotates in response to a printing command, the power of the motor is transmitted to the cam through the series of reduction gears so that the cam is rotated, thereby causing the paper loading tray, which supports sheets of paper therein, to be lifted. If the sheets of paper reach a predetermined height and a sensor detects the height of the sheets of paper, the operation of the motor is stopped by a detecting signal from the sensor. Then, the sheets of paper are picked up one by one by a pickup roller and fed to a printing unit. If the sheets of paper have a reduced height by continuing the paper feeding operation and the sensor detects the reduced height, the operation of the motor is resumed by a detecting signal from the sensor, such that the paper loading tray is lifted as high as the sheets of paper are discharged.
However, the above described conventional image forming apparatus has a problem of high manufacturing costs and great consumption of electric power because of the separate motor required to lift or lower the paper loading tray. Further, the conventional image forming apparatus has no means for dealing with malfunction of the sensor that is used to detect the height of sheets of paper, or failure in the control of the motor due to unexpected reasons. Therefore, if excessive power is transmitted from the motor under an abnormal situation, there is a high risk of damage to constituent elements of the image forming apparatus.